How to increase the bus density?

If you don't mind using mods, there are some of them that deals with that problem. I would recommend using Improved Public Transport that gives you more control over your transport lines.

This mods allows to set the capacity for each kind of public transport and to manage the number of vehicles for each line. As you increase the vehicles' capacities, the maintenance cost are also increased accordingly.

Alternatives to this mod :

• Configurable Transport Capacity
• Improved Transport Capacity (deprecated)

The answer for you is probably going to be some combination of all of the above depending on your situation, so let's go through bit by bit:

A) Adding more stops would spread out the passengers, and C:S calculates the number of buses used by a line based on its length. This bleeds into B, C, and D. Do you want many short lines with a fewer buses? Or fewer long lines with lots of buses? I'd err on the side of a larger number of smaller lines. It will divide your passengers up between the lines based on where exactly it is they're trying to go. Intersecting these lines will allow them to hop from line to line more efficiently.

E) As far as I know, adding additional bus depots does not increase the number of buses spawned. The only reason you might want to do this is to decrease the initial transit time of the buses when you create a new line.

F) Yes, adding more to your bus budget will increase the number of buses allocated to your lines. This is the easiest, most surefire option, but also the most heavy handed and expensive.

Here's a SimNation article that goes into more depth on some of these topics.

Since the free update which came with the release of the Public Transportation DLC you can now adjust the budget of bus lines (or any kind of public transportation line, for that matter) individually, which will affect the number of vehicles used on that line.

1. Open the "Transport" map mode
2. Click on "Lines Overview"
3. Click on the magnifying glass next to the line you want to adjust
4. Use the "vehicle count modifier" slider to assign more or less budget to the line, resulting in more or less vehicles.

Keep in mind that it uses the mechanic of the regular budget panel: the further you go away from 100% (in either direction), the more you pay for each vehicle. So if you feel the need to crank it up a lot, it might be better to add more bus lines instead.